Fully redundant position sensor

ABSTRACT

A position sensor according to some embodiments includes a first position sensor board having first sensor coils and a first transmit coil; a second position sensor board having second sensor coils stacked with, and separated from by a distance Z, the first position sensor; and at least one target positioned relative to the stacked first position sensor and second position sensor. A redundant position sensor according to some embodiments includes a plurality of stacked sensor boards, each of the plurality of sensor boards including sensor coils, wherein one of the plurality of stacked sensor boards includes an active transmit coil; and a target positioned over the plurality of stacked sensor boards.

RELATED APPLICATION

The present application claims priority to Provisional PatentApplication Ser. No. 62/725,185, entitled “Fully Redundant PositionSensor,” by Gentjan Qama and Maria Agalidis, filed on Aug. 30, 2018,which is herein incorporated by reference in its entirety.

TECHNICAL FIELD

Embodiments of the present invention are related to position sensorsand, in particular, to redundant position sensors.

DISCUSSION OF RELATED ART

Position sensors are used in various settings for measuring the positionof one component with respect to another. Inductive position sensors canbe used in automotive, industrial and consumer applications for absoluterotary and linear motion sensing. In many inductive positioning sensingsystems, a transmit coil is used to induce eddy currents in a metallictarget that is sliding or rotating above a set of receiver coils.Receiver coils receive the magnetic field generated from eddy currentsand the transmit coils and provide signals to a processor. The processoruses the signals from the receiver coils to determine the position ofthe metallic target above the set of coils. The processor, transmitter,and receiver coils may all be formed on a printed circuit board (PCB).

However, these systems exhibit inaccuracies for many reasons. Forexample, the electromagnetic field generated by the transmitter, and theresulting fields generated in the metallic target, may be non-uniform,the connections of wire traces to the transmit coils and the arrangementof receive coils may result in further non-uniformity. The air-gap (AG)between the metallic target and the coils mounted on the PCB may benon-uniform. Further, the amplitudes of signals generated by receivercoils may have an offset. There may be mismatches between the multiplereceiver coils. There may be different coupling effects between themetallic target and each of the multiple receiver coils. These and otherfactors may result in inaccurate results of the position locatingsystem.

Therefore, there is a need to develop better methods of designing sensorcoils that offer better accuracy for position sensing.

SUMMARY

In some embodiments, a position sensor design is provided. A positionsensor according to some embodiments includes a first position sensorboard having first sensor coils and a first transmit coil; a secondposition sensor board having second sensor coils stacked with, andseparated from by a distance Z, the first position sensor; and at leastone target positioned relative to the stacked first position sensor andsecond position sensor.

A redundant position sensor according to some embodiments includes aplurality of stacked sensor boards, each of the plurality of sensorboards including sensor coils, wherein one of the plurality of stackedsensor boards includes an active transmit coil; and a target positionedover the plurality of stacked sensor boards.

These and other embodiments are discussed below with respect to thefollowing figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a coil system for determining a position of a target.

FIGS. 2A and 2B illustrate a position sensor according to someembodiments of the present invention.

FIG. 3 illustrates a linear sensor board that can be used in theposition sensor illustrated in FIG. 2A.

FIGS. 4A and 4B illustrate an angular position sensor board that can beused in the position sensor illustrated in FIG. 2A.

FIGS. 5A and 5B illustrate an arc positions sensor board that can beused in the position sensor illustrated in FIG. 2A.

FIGS. 6A and 6B illustrate a stacked 360 degree rotary stacked positionsensor according to some embodiments.

FIGS. 6C, 6D, 6E, and 6F illustrate some test data regarding the 360degree rotary stacked position sensor as illustrated in FIGS. 6A and 6B.

FIGS. 7A and 7B illustrate a stacked linear position sensor according tosome embodiments using linear position boards similar to thoseillustrated in FIG. 3.

FIGS. 7C, 7D, 7E, and 7F illustrate data regarding the stacked linearposition sensor according to some embodiments.

FIGS. 8A and 8B illustrated a stacked angular position sensor.

FIGS. 8C, 8D, 8E, and 8F illustrate data regarding the angular positionsensor illustrated in FIGS. 8A and 8B.

FIGS. 9A, 9B, 9C, and 9D illustrate another example of a stackedposition sensor according to some embodiments.

These and other aspects of embodiments of the present invention arefurther discussed below.

DETAILED DESCRIPTION

In the following description, specific details are set forth describingsome embodiments of the present invention. It will be apparent, however,to one skilled in the art that some embodiments may be practiced withoutsome or all of these specific details. The specific embodimentsdisclosed herein are meant to be illustrative but not limiting. Oneskilled in the art may realize other elements that, although notspecifically described here, are within the scope and the spirit of thisdisclosure.

This description illustrates inventive aspects and embodiments shouldnot be taken as limiting—the claims define the protected invention.Various changes may be made without departing from the spirit and scopeof this description and the claims. In some instances, well-knownstructures and techniques have not been shown or described in detail inorder not to obscure the invention.

Embodiments of the present invention utilize stacked sensor boards toprovide redundant measurements of the position of a target positionedover the stacked sensor boards. Each of the boards includes sensorcoils, usually a sin coil and a cos coil. At least one of the boards hasan active transmit coils. One transmit coil on one of the stacked boardsis powered while the remaining transmit coils are shorted so as to beinoperative or, in some embodiments, do not exist. The measurement ofsignals from multiple stacked sets of sensor coils on the stacked sensorboards can then be used to provide redundant signals from which a moreaccurate measure of the position of a target positioned over the stackedboards can be made.

In a redundant sensor, for example one used in automotive application,the system sensors should remain working when one or more of thetransmitters is shorted for any reason, as is the case in embodiments ofthe present invention. The issue that occurs when a transmitter isshorted is a result of coupling between the transmitters. When onetransmitter is shorted the magnitude is damped down, for example to 70%of its full value. Embodiments of the present invention providessolutions for handling or controlling the damping of the magnitude as aresult of these interactions between transmit coils.

FIG. 1 illustrates a positioning system 100. As illustrated in FIG. 1,the positioning system includes a transmit/receive control circuit 102that is coupled to drive a transmitter coil 106 and receive signals fromreceive coils 104. In most configurations, receive coils 104 are formedon a printed circuit board (PCB) within transmitter coil 106, which isalso formed on the PCB. In FIG. 1, for purposes of clarity, transmitcoil 106 and receive coils 104 are illustrated separately. Receive coils104 are generally physically located within a border formed by transmitcoil 106. As is illustrated in FIG. 1, transmit coils 106 are driven togenerate a magnetic field 108. Magnetic field 108, with the positivecurrent illustrated by the arrows, is circular around each wire and in adirection that points out of the page inside coil 106 and into the pageoutside of coil 108 with the current direction as illustrated in FIG. 1.In general, transmit coil 106 is driven to provide a time-varyingmagnetic field 108. The time-varying magnetic field 108 interacts with aconductive target (not shown), which then induces a response in receivecoils 104. The position of conductive target over receive coils 104 canbe determined by the response induced in receive coils 104.

FIG. 2A illustrates a positioning system 200 according to someembodiments of the present invention. As illustrated in FIG. 2A,positioning system 200 includes a sensor board stack 210. Sensor boardstack 210 includes N sensor boards 202 (sensor boards 202-1 through202-N). Each of sensor boards 202 includes sensor coils, usually a sincoil and a cos coil. Further, each of sensor boards 202 may include atransmit coil, although in some embodiments only one sensor board 202,sensor board 202-i illustrated in FIG. 2A, may have a transmit coil. Inembodiments where all of sensor boards 202 include a transmit coil, thetransmit coil on all of sensor boards 202 except for sensor board 202-iare shorted and therefore become ineffective. In embodiments of thepresent invention, N is any integer that is two (2) or greater (N≥2)while i identifies whichever one of boards 202-1 through 202-N has anactive transmit coil (1≤i≤N).

As is illustrated in FIG. 2A, in some embodiments spacers 204 canprovide spacing between adjacent ones of sensor boards 202. In someembodiments, sensor coils may be arranged on opposite sides of amulti-layer PCB board such that the spacing between sensor coils 204corresponds to the board thickness. In such case, spacers 204 may not beincluded and boards 202 may be bonded to each other. As illustrated inFIG. 2A, the spacing between boards 202-1 and 202-2 can be Z1, forexample. The spacing between boards 202-(N−1) and 202-N is Z(N−1). Insome embodiments, the spacing between adjacent boards can be differentso that spacings Z1 through Z(N−1) may all be different. However, insome embodiments, the spacings may all be the same and designated asspacing Z.

As is further illustrated in FIG. 2A, target 206 is positioned to moveover the top sensor board 202 in stack 210. Transmit coils on one ofboards 202-1 through 202-N in stack 210 are energized. As illustrated inFIG. 2A, the transmit coils in board 202-i is energized while anytransmit coils in the remainder of boards 202 is rendered ineffective,usually by shorting the ineffective transmit coils. As further discussedbelow, sensor coils on each of boards 202 in stack 210 provide signalsindicative of the position of target 206 over each of boards 202-1through 202-N.

As is further illustrated in FIG. 2A, a stack control circuit 208 iscoupled to each of boards 202 in stack 210. As is illustrated in FIG.2A, stack control circuit 208 is coupled to sensor coils on each ofboards 202-1 through 202-N and is coupled to control the drive of thetransmit coil on board 202-i. In some embodiments, stack control circuit208 may be coupled directly to coils on each of boards 202-1 through202-N. In some embodiments, stack control circuit 208 may be coupled tocircuits on each of boards 202-1 through 202-N that are then coupled tocoils on those boards. Stack control circuit 208, therefore, controlsthe drive of the transmit coil on board 202-i and receives sensorsignals, usually a sin coil signal (RS) and a cos coil signal (RC), fromeach of boards 202-1 through 202-N. From the signals from the sensorcoils, stack control circuit 208 determines the position of target 206relative to boards 202-1 through 202-N of stack 210.

FIG. 2B illustrates an example embodiment of a processing circuit 218,which can include stack control circuit 208 and other circuitry that maybe present on individual boards 202-1 through 202-N. Consequently, insome embodiments, some functions illustrated in processing circuit 218illustrated in FIG. 2B can be performed on circuitry on individual onesof boards 202-1 through 202-N.

As illustrated in FIG. 2B, processing circuit 218 includes individualcircuits 240-1 through 240-N, each of which processes the receivesignals RC1, RS1 through RCN, RSN from each of boards 202-1 through202-N, respectively. The signals RC1, RS1 through RCN, RSN refers to thecosine configured receive coil signals (RCj) and the sine configuredreceiver coil signals (RSj) from board 202-j, where 1≤j≤N.

Considering circuit 240-1 specifically as an example, receiver signalsRC1 and RS1 are received in an analog front end (AFE) 220-1. Signals RC1and RS1 may be received in a multiplexer 222-1 in AFE 220-1, which maytime-division multiplex the input signals. In some embodiments, each ofreceiver signals RC1 and RS1 can be processed by parallel circuits inprocessing circuit 240-1.

As shown in FIG. 2B, the output signal from multiplexer 222-1 is inputto a rectifier 224-1, which rectifies the signals RC1 and RS1 to providerectified signals. The rectified signals are then input to gain stagecircuit 226-1. Gain stage circuit 226-1 can provide controlledamplification of the rectified signals. Each gain stage in gain circuit226-1 can increase the magnitude so that the rectified signal isincreased by a factor (√{square root over (2)})^(GS), where GS is thenumber of gain stages. Any number of gain stages GS can be used. In someembodiments, the number of gain stages GS can be controlled by a digitalprocessing circuit 234-1, which is further discussed below.

The amplified signal from gain stage circuit 226-1 is then input tointegrator 228-1. Integrator circuit 228-1 integrates the signals fromgain stage 226-1 over an effective integration time given by(7+ext)*lc_period, where lc_period=1/LC. The period 1/LC represents thetank frequency of the receive coil inductance and a tank capacitor.When, as described above, the frequency is increased during a short ofthe transmit coils, the lc_period also decreases, which also decreasesthe effective integration time. The gain of integrator 228-1 is thenproportional to the effective integration time. The parameter ext is acontrollable extension parameter, which again can be set in digitalpre-processing 234-1 as discussed below.

In some embodiments, gain stages 226-1 and integrator 228-1 may beinterchanged from that shown in FIG. 2B. In those embodiments, thesignals from rectifier 224-1 are first integrated in integrator 228-1and then amplified in gain stages 226-1.

The output signals from integrator 228-1 is then input to asample-and-hold circuit 230-1. An Analog-to-Digital Converter (ADC)232-1 then receives and digitizes the held signals from sample-and-holdcircuit 2301. The digitized signals from ADC 232-1 are input to adigital processing circuit 234-1, which may provide further digitalprocessing. Further filtering may be performed in digital processingcircuit 234-1. Furthermore, digital processing circuit 234-1 providessignals (e.g., GS and ext) that control gain stage circuit 226-1,integrator 228-1, and multiplexer 222-1. These parameters can bedetermined in digital processing circuit 234-1 by monitoring theprocessed and digitized signals RC1 and RS1 received from the receivercoils and adjusting gains and integration times accordingly. The signalfrom processing 234-1 can then be provided to a Coordinate Rotation byDigital Computer (CORDIC) 236-1. CORDIC 236-1 receives the processedsignals RC1 and RS1 and provides the angle signal Angle1. In someembodiments, the functions of digital processing circuit 234-1 andCORDIC 236-1 can be performed on a microcontroller that includes digitalprocessors and memory (volatile and non-volatile) that holds data andprogramming instructions to be executed on the digital processors.

As is further illustrated in FIG. 2B, each of circuits 240-1 through240-N include the same components. Multiplexer 222-N, rectifier 224-N,gain stages 226-N, integrator 228-N, and sample-and-hold 230-N of AFE220-N operate as described above with respect to the multiplexer 222-1,rectifier 224-1, gain stages 226-1, integrator 228-1, andsample-and-hold 23-N of AFE 220-1 described above. Similarly, ADC 232-N,digital pre-processing 234-N, and CORDIC 238-N operate as describedabove with respect to ADC 232-1, digital pre-processing 234-1, andCORDIC 238-1 as described above.

Processing 240 receives the angle determinations Angle1 through AngleNfrom circuits 240-1 through 240-N, respectively. Processing 240 thendetermines the positioning of target 206 based on the angles Angle1through AngleN. Processing 240 can also be executed on amicrocontroller, which may be the same microcontroller discussed aboveor a different microcontroller.

FIG. 3 illustrates a configuration of transmit coil 306 and receivecoils 304 on a board 300, which in this example is a linear positionlocating board 300. For reference, a conductive metallic target 324 isillustrated positioned over board 300. In operation, transmit coil 306can be driven to form a magnetic field if board 300 corresponds to board202-i in stack 204, otherwise transmit coil 306 may be removed orshorted. Transmit coil 306 can be driven at a range of frequencies or atparticular frequencies to create a time-varying magnetic field. Receivecoils 304 are located inside coil 306. Transmit coil 306 is driven atany frequency that can produce electromagnetic fields that result,through a target 324, in induced voltages in receiver coils 304. Ingeneral, there can be any number of receiver coils 304, however, forease of discussion, a system with two receiver coils, a sin coil and acos coil, is discussed below.

FIG. 3 illustrates the arrangement of sensor receive coils (RX) 304within transmit coil (TX) 306. As illustrated in FIG. 3, sensor receivecoils 304 includes a sin-wave oriented coil RX SIN 312 and acos-oriented signal coil RX COS 310. Sin-wave oriented coil RX SIN 112includes sin loops 314, 316, and 318 where coil 312 is wound in in-phaseor anti-phase directions, here depicted as clockwise or counterclockwise depictions, to result in the production of voltages in theloop of opposite sign as a result of the presence of theelectro-magnetic field generated by transmit coil 306. As isillustrated, the wiring of sin-wave oriented coil 312 provides aclockwise rotation in loops 314 and 318 resulting in a nominallypositive voltage and a counterclockwise rotation in loop 316 resultingin nominally negative voltages. Similarly, cos oriented coil 310 mayinclude a first loop 320 with a clockwise orientation and a second loop322 with a counterclockwise orientation FIG. 3 illustrates a possibleelectromotive force reference direction, as indicated by the arrows,that is consistent with the magnetic fields produced by transmitter coil306 in the period when the magnetic field generated by transmit coil 306is into the page on the inside of transmit coil 306 and out of the pageoutside of the area defined by transmit coil 306. This is opposite whenthe time varying magnetic field driven by a time varying current intransmit coil 306 is oriented otherwise.

In some embodiments of the present invention, board 300 can be used asone of boards 202-1 through 202-N of stack 210 as illustrated in FIG. 2,the transmitter coil (TX) 306 is stimulated by the circuit 340 asdirected by stack control circuit 208 if board 300 is board 202-i.Otherwise, transmit coil 306 is shorted or absent. As discussed above,stack control circuit 208 may be an integrated circuit that directs acurrent to transmit coil 306 of board 202-i, which generates a variableElectromagnetic field (EMF). The EMF couples with the receiver coils(RX) 304. If a conductive metallic target 324 is placed on the top ofthe receiver coils 304 as illustrated in FIG. 3, an eddy current isgenerated in the metallic target 324. This eddy current generates a newelectromagnetic field that is ideally equal and opposite of thegenerated EMF, canceling the field in receiver coils 304 directly undermetallic target 324. The receiver coils (RX) 304 capture the variableEMF field generated by the transmit coils 306 and those induced bymetallic target 324, resulting in sinusoidal voltages generated at theterminals of receiver coils 304. Signals related to those voltages (RCand RS), as illustrated in FIGS. 2A and 2B, are input to stack circuit208.

As discussed above, stack control circuit 208 and circuit 340 togetheroperate to drive a transmit coil and receive signals from each set ofsensor coils 304. As such, circuit 208 includes sufficient processing toreceive and analyze sensor signals from circuit 340. Amplification anddigitization can be performed in an analog-front-end (AFE) circuit 220that is located in circuit 340, may be performed in circuit 208, or maybe split between the two circuits. In some embodiments, circuit 340 mayinclude circuit 240 (one of circuit 240-1 through 240-N as shown in FIG.2B) while circuit 208 may include processing 240 as illustrated in FIG.2B. Consequently, circuit 208 receives the angle signals Angle1 throughAngleN from CORDICs 236-1 through 236-N, which are included in circuits340-1 through 340-N of boards 202-1 through 202-N, respectively.

In the absence of metallic target 324, there will be no voltage at theterminals of the RX coils 304—labeled Rx COS 310 (RC) and RX Sin 312(RS) in FIG. 3. When metallic target 324 is placed in a specificposition with respect to the RX coils 304, the resultant electromagneticfield on the area covered by the metallic target 324 is ideally zero andtherefore the voltages at the terminals of the RX coils 304 will havedifferent characteristic depending on the location of metallic target324 relative to receiver coils 304. The RX coils 304 provide a sinvoltage that is created at the terminals of one RX coil (Rx Sin 312) anda cos voltage that is created at the terminals of the other RX coil (RxCos 310) as metallic target 324 is swept across receiver coils 304. Theposition of the target 324 with respect to the RX coils 304 modulatesthe amplitude and the phase of the voltage at the terminals of the RXcoils 304, RC and RS.

As illustrated in FIGS. 2A and 2B, an on-board circuit 340 asillustrated in FIG. 3 can receive signals from stack control circuit208, drive transmit coil 306 (if it is driven on that board), andreceive signals from sensor coils 304. As discussed above, transmittercoil 306, receive coils 304, and a circuit 340 can be mounted on asingle printed circuit board. Further, the PCB can be positioned suchthat metallic target 324 is positioned above receive coils 304 andspaced from receive coils 304 by a particular spacing, usually referredto as the air gap (AG). The position of metallic target 324 relative tothe PCB on which receive coils 304 and transmitter coil 306 is mountedcan be determined by processing the signals generated by sin-orientedcoil 312 and cos-oriented coil 310.

As shown in FIG. 2A with N=2, in accordance with some embodiments of thepresent invention, a position sensor 200 can be formed by stacking twoidentical position sensor boards and shorting the transmitter coil ofone of the stacked position sensor boards. As described above, aposition sensor is formed with a transmission coil and, usually, twosensor coils. Stacking two positions sensors, while shorting thetransmitter coil of one of them, provides redundancy in the positionsensor coils that can result in more accurate measurement of theposition of a target 206.

In some embodiments, four-layer board designs can be provided. In afour-layer board design, two sensor boards 202 (each with two layers)are stacked so that the distance between sensor coils 204 is given bythe thickness of the printed circuit board layers. General observationshave been formed from data taken using these board designs. Theseobservations are 1) that the operating frequency is doubled when the Txcoil is shorted; 2) that the remaining active device whose coil is notshorted is functional, but the carrier frequency of the oscillation hasdoubled; 3) that having a doubled frequency means the signal magnitudeis divided by two (2) due to the analog-front-end (AFE) integration inintegrator 228-1; 4) that in order to compensate the magnitude loss dueto frequency change, the integration cycle needs to be increased; and 5)that the gain stage (GS) of the processing circuitry needs to increaseby two (2) additional stages to have the remaining active devicefunction properly.

The stacked sensor boards 202 can be linear position sensor boards 300as illustrated in FIG. 3. FIGS. 4A and 4B illustrate an angular positionboard 400 that can be used as stacked boards 202. FIG. 4A illustratesthe back side of a position sensor board 400 and FIG. 4B illustrates thefront side of a position sensor board 400. As illustrated in FIGS. 4Aand 4B, transmit coil 406 and sensor coils 404 are positioned in an arc.Circuit 410, which interfaces with stack controller 208, can be mountedalong with coils 404 and 406 on printed circuit board 402. As discussedabove, circuit 410 may be configured as a circuit 240 (one of circuits240-1 through 240-N) as illustrated in FIG. 2B.

FIGS. 5A and 5B illustrate two identical stacked arc position sensorboards 500 that can be used as stacked boards 202. As illustrated,transmit coil 506 and sensor coils 504 are positioned in an arc. Circuit510, which interfaces with stack controller 208, can be mounted alongwith coils 504 and 506 on printed circuit board 502. As discussed above,circuit 510 may be configured as a circuit 240 as illustrated in FIG.2B.

In a typical design of embodiments of the present invention, sensorcoils and transmit coil are designed on four (4) layer boards. Twosymmetric coil designs can then be stacked and separated by thethickness of the printed circuit board (PCB) itself. The operatingfrequency range can be controlled to stay within particularspecifications, for example as determined by the needs of a datasheet.The distance between the two-coil design on top and bottom influence afrequency increase. Consequently, the frequency can be controlled by thethickness of the PCB, or as illustrated in FIG. 2A by spacers betweenadjacent ones of boards 202. The magnitude of the measured signals canbe controlled by adjusting the automatic integration cycle (ext) and theautomatic gain control (GS) in the circuit 218, which is implementedbetween circuits on boards 202 and stack circuit 208.

Consequently, some embodiments of the present invention include two PCBsensors with the same geometry stacked as illustrated in FIG. 2A. In oneof the two PCB sensors, the transmitter is shorted. In some embodiments,the distance Z between boards 202 is defined as the thickness of PCBboards 202.

FIGS. 6A and 6B illustrate a stacked 360-degree position sensor 600according to some embodiments of the present invention. FIG. 6Aillustrates a bottom PCB board 602 on which transmit coil 606 and360-degree sensor coils 604 are illustrated. In sensor 600, transmitcoil 606 on board 602 is shorted to make it ineffective. Transmissioncoil 606 and sensor coils 604 are coupled to circuitry 610, which can becoupled to a stack controller circuit 208 as shown in FIGS. 2A and 2B.FIG. 6B illustrates the top PCB board 612. PCB board 612 includes sensorcoils and transmission coils that are symmetrical with transmission coil606 and sensor coils 604 illustrated in FIG. 6A. Further, as shown,circuitry 620 on board 612 can also be coupled to stack controllercircuit 208 as illustrated in FIG. 2B. The transmission coil on PCBboard 612 is active. As is further illustrated in FIG. 6B, an insulatedspacer 616 separates the sensors on board 612 from a target 614, whichis rotated with a knob 618. Using stacked position sensor 600 asillustrated in FIGS. 6A and 6B, test data was taken under variousoperating conditions and spacing Z between positions sensors on boards602 and 612. The test data is further described below.

FIG. 6C illustrates measurement of the oscillation frequency as afunction of separation Z for position sensor 600 as illustrated in FIGS.6A and 6B. As is illustrated in FIG. 4C, the following frequency data,measured with an oscilloscope during operation of the sensor, wasobtained (“Inf” referring to the condition where board 602 is removed):

Z (mm) Frequency f (MHz) 0 5.6 1 4.5 2 4.2 3 3.9 4 3.75 Inf. 3.6

The CORDIC Magnitude can be read from a register of the circuit thatincludes the CORDIC 236 or from a processor that executes that function.In this example, CORDICs 236-1 and 236-2 are included in circuits 610and 620, respectively. FIG. 6D illustrates the CORDIC magnitude as afunction of Z for the embodiment illustrated in FIGS. 6A and 6B. Thetarget 614 was fixed at a 1 mm distance (air gap) on top of thenon-shorted transmit coil PCB 612. The actual position of target 614 onthe rotary is not important as the magnitude is constant in the overallmeasurement range. With a gain stage (GS) of 8 and integration parameterEXT of 3, the following data was obtained:

Z (mm) Magnitude M 0 2900 1 4900 2 5300 3 6180 4 7100 Inf. 7800

FIG. 6E illustrates the CORDIC magnitude as a function of Z for theembodiment illustrated in FIGS. 6A and 6B. The target 614 was fixed at a1 mm distance (air gap) on top of the non-transmit coil shorted PCB 612.The actual position of the target on the rotary is not important as themagnitude is constant in the overall measurement range. With a gainstage (GS) of 8 and integration parameter EXT of 13, the following datawas obtained:

Z (mm) Magnitude M 0 6094 1 9154 2 11050 3 12900 4 14100 Inf. 15600FIG. 6F compares the EXT=3 data of FIG. 6D and the EXT=13 data of FIG.6E.

FIGS. 7A and 7B illustrate illustrates a linear redundant positionsensor formed by stacking two PCBs such as that shown in FIG. 3 withidentical linear position sensors. As shown in FIGS. 7A and 7B, boards300-1 and 300-2 are stacked to form stacked linear position sensor 700.FIG. 7A illustrates board 300-1 with transmission coil 306-1, which isshorted, along with sensor coils 304-1 as described in FIG. 3. Circuit320-1 is coupled to transmission coil 306-1, sensor coil 304-1, andprovides signals to circuit 208 as illustrated in FIG. 2. FIG. 7Billustrates linear sensor board 300-2, with transmission coil 306-2 andsensor coils 304-2. Transmission coil 306-2 is an active (or notshorted) transmission coil. Circuit 320-2 is coupled to transmissioncoil 306-2 and sensor coils 304-2, drives transmission coil 306-2, andprovides signals to circuit 208 as illustrated in FIG. 2.

FIG. 7C illustrates a graph of frequency versus Z. The observed data isprovided as follows:

Z (mm) Frequency f (MHz) 0 4.7 1 3.95 2 3.6 3 3.4 4 3.28 Inf. 3.15

The following experimental data consists in measuring the CORDICmagnitude (e.g., reading the value from the register). The target isfixed with a 1 mm distance (air gap) on top of the board 300-2, whichhas the non-shorted transmit coil.

FIG. 7D illustrates the CORDIC Magnitude as a function of Z where thegain stage (GS) is 11 and the integration parameter EXT is 3. The datais provided as follows:

Z (mm) Magnitude M 0 2400 1 4200 2 5500 3 6380 4 6800 Inf. 7300

FIG. 7E illustrates CORDIC Magnitude data versus Z with the systemillustrated in FIGS. 7A and 7B with a gain stage (GS) of 11 andintegration parameter EXT of 13. The data is provided as follows:

Z (mm) Magnitude M 0 4500 1 8300 2 9500 3 10500 4 13000 Inf. 15000FIG. 7F illustrates a comparison of the data illustrated in FIGS. 7D and7E.

FIGS. 8A and 8B illustrates another example of a stacked position sensorsystem 800 based on the sensor boards 500 illustrated in FIGS. 5A and5B. FIG. 8A illustrates position sensor board 500-1 transmission coil506-1 and sensor coils 504-1 coupled to circuit 510-1. In this example,transmission coil 506-1 is shorted. FIG. 8B illustrates board 500-2 withtransmission coil 506-2 and sensor coils 504-2 coupled to circuit 510-2.In this example, transmission coil 506-2 is active.

FIG. 8C illustrates the frequency versus Z for the stacked positionsensor system illustrated in FIGS. 8A and 8B. The frequency data isprovided as follows:

Z (mm) Frequency f (MHz) 0 2.96 1 2.4 2 2.140 3 2.01 4 1.9 Inf. 1.67

The following data consists in measuring the CORDIC magnitude (e.g.,reading the value from the register). The target was fixed with a 2 mmdistance (air gap) on top of the non-shorted transmission coil side ofthe position sensor.

FIG. 8D illustrates the CORDIC magnitude as a function of Z for a systemwith gain stage (GS) of 5 and integration parameter EXT of 3. The datais provided below:

Z (mm) Magnitude M 0 2900 1 4080 2 5800 3 6900 4 8100 Inf. 10800

FIG. 8E illustrates the CORDIC magnitude as a function of Z for a systemwith gate stage (GS) of 5 and Integration parameter EXT of 13. The datais provided below:

Z (mm) Magnitude M 0 5850 1 9160 2 11100 3 12470 4 13200 Inf. 14350FIG. 8F illustrates a comparison of the data in FIGS. 6D and 6E.

With regard to the fixing the target in a redundant system such as thatshown in FIGS. 8A and 8B. In some cases, the target is positioned on thetop of the stacked PCBs. In some embodiments, the magnitude measuredGS=5, Air gap=5 mm, and magnitude=5700. In another orientation, thetarget can be positioned on the bottom of the stacked PCBs with GS=5,air gap-=3 mm, and resulting magnitude of 10700. Options for the targetpositions includes using two targets. If the receivers are very close toeach other, a single target can be used. In the above description, ifonly one target is used the gain stage automatic gain can be turned on.

FIGS. 9A, 9B, 9C, and 9D illustrate another embodiment of stackedposition sensor 900 according to some embodiments of the presentinvention. Although FIGS. 9A, 9B, 9C, and 9D illustrate a 360-degreeposition sensor, the position sensor may be an angular position sensoror a linear sensor.

FIG. 9A illustrates one board 902-1. Board 902-1 includes transmit coil906-1, receiver coils 904-1, and circuit 910-1 mounted on a four-layerprinted circuit board 912-1. As is illustrated, transmitter coil 906-1is provided on two layers while receive coils 904-1 are provided on theother two layers.

Similarly, FIG. 9B illustrates a second board 902-2. Board 902-2includes transmit coil 906-2, receiver coils 904-2, and circuit 910-2mounted on a four-layer printed circuit board 912-2. As illustrated,transmitter coil 906-2 is provided on two layers while receive coils904-1 are provided on the other two layers.

As illustrated in FIGS. 9A and 9B, transmit coil 906-2 has a greaterdiameter than does transmit coil 906-1. Receive coils 904-1 and 904-2are the same. In embodiments of the present invention, the relativediameters of transmit coils between coils may vary. The relative sizesof receive coils between stacked boards may also differ, but in mostembodiments is the same.

FIGS. 9C and 9D illustrates formation of stacked position sensor 900. Asillustrated in FIG. 9C, board 902-1 and board 902-2 are oriented suchthat transmit coils 906-1 and 906-2 are on the outside of the resultingsensor 900 while receive coils 904-1 and 904-2 are closer together onthe inside of sensor 900. Boards 902-1 and 902-2 are separated by aspacer 914, which can be another printed circuit board.

FIG. 9D further illustrates the separation distances. As illustrated inFIG. 9D, sensor boards 902-1 and 902-2 are separated by a spacer 914.Board 902-1 is positioned such that transmit coil 906-1 is on top andreceive coils 904-1 are close to spacer 914. Similarly, board 902-2 isoriented such that receive coils 904-2 are close to spacer 914 andtransmit coils 906-2 are on the bottom. Consequently, receive coils904-1 and 904-2 are separated by a distance dRx. Transmit coils 906-1and 906-2 are separated by a distance DTx.

A target 916 is illustrated positioned over sensor board 902-1. Thisresults in an air gap between receiver coils 904-1 and target 916 of AGA and an air gap between receiver coils 904-2 and target 916 of AG B.

The larger the distance RX-TX on sensor 900, the higher is the magnitudewhen one of the transmitters is shorted. When shorted, a transmit coil906 operates as a target for the sensors. With regard to sensor board902-2, for example, the board thickness may be 1 mm, which results in adistance between receiver coil 904-1 and transmit coil 906-2 of 2 mm,where spacer 914 also has a thickness of 1 mm.

Consequently, in some embodiments of redundant systems according to thepresent invention, two position sensors are stacked and one of thetransmit coils is shorted. The solution is based on the topologicalplacement of the TX, RX, and target. Further illustrated in theconfiguration of FIG. 9D, transmit coil 906-1 would be active andtransmit coil 906-2 is inactive.

The above detailed description is provided to illustrate specificembodiments of the present invention and is not intended to be limiting.Numerous variations and modifications within the scope of the presentinvention are possible. The present invention is set forth in thefollowing claims.

What is claimed is:
 1. A position sensor, comprising: a first positionsensor board having first sensor coils and a first transmit coil; asecond position sensor board having second sensor coils and secondtransmit coil stacked with, and separated from by a distance Z, thefirst position sensor; and at least one target positioned relative tothe stacked first position sensor and second position sensor, whereinthe second transmit coil is shorted while the first transmit coil isactive.
 2. The position sensor of claim 1, wherein the first sensorcoils of the first position sensor board and the second sensor coils ofthe second position sensor board are symmetrical.
 3. The position sensorof claim 2, wherein the first sensor coils includes a first sin-orientedcoil and a first cos-oriented coil and the second sensor coils includesa second sin-oriented coil and a second cos-oriented coil.
 4. Theposition sensor of claim 1, wherein the first position sensor board andthe second position sensor board are each linear position boards.
 5. Theposition sensor of claim 1, wherein the first position sensor board andthe second position sensor board are each angular position boards. 6.The position sensor of claim 1, wherein the first position sensor boardand the second position sensor board are each 360-degree positionboards.
 7. The position sensor of claim 1, wherein the first positionsensor board includes a first controller circuit coupled to drive thefirst transmit coil and receive signals from the first sensor coils andwherein the second position sensor board includes a second controllercircuit coupled to receive signals from the second sensor coils.
 8. Theposition sensor of claim 7, further including a stack controller circuitcoupled to the first controller circuit and the second controllercircuit.
 9. The position sensor of claim 8, wherein the first controllercircuit comprises a first gain stage circuit that receives the signalsfrom the first sensor coils, the first gain stage circuit providing afirst amplified signal; an integration circuit that receives the firstamplified signal and provides a first integrated signal; ananalog-to-digital converter that receives the first integrated signal;and a CORDIC circuit that provides a first angle measurement from thefirst integrated signal.
 10. The position sensor of claim 8, wherein thestack controller circuit receives a first angle measurement from thefirst controller circuit and a second angle measurement from the secondcontroller circuit and is configured to determine a position of thetarget.
 11. The position sensor of claim 1, wherein the target ispositioned closest to the first position sensor board and the transmitcoil of the first position sensor is active.
 12. A redundant positionsensor, comprising: a plurality of stacked sensor boards, each of theplurality of sensor boards including sensor coils, wherein at least oneof the plurality of stacked sensor boards includes a transmit coil, anda target positioned over the plurality of stacked sensor boards, whereinone or more of the plurality of stacked sensor boards includes atransmission coil, wherein the transmission coil for each of theplurality of boards except for the one with the active transmit coil isshorted.
 13. The redundant position sensor of claim 12, wherein theplurality of stacked sensor boards includes two stacked sensor boards.14. The redundant position sensor of claim 12, wherein the plurality ofsensor boards are linear position boards.
 15. The redundant positionsensor of claim 12, wherein the plurality of sensor boards are angularposition boards.